Carrier-current relaying



Jan. 17, 1939. B E LENEHAN 2,144,499

CARRIER-CURRENT RELAYING Filed Dec. 1, 1937 2 Sheets-Sheet l CSP 192% C W y- I Bernard Elena/70h ATTORNEY Jan. 17, 1939.

ZZL-EL Receive/ g WITNESSES:

B. E. LENEHAN CARRIER-CURRENT RELAYING Filed Dec. 1,

2 Sheets-Sheet 2 INVENTOR I fier/mm f. [eve/van BY 5 I g z ATTORNEY Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE CARRIER-CURRENT RELAYING of Pennsylvania Application December 1, 1937, Serial No. 177,475

25 Claims.

My present invention is an improvement over the pilot protective systems which are described and claimed in a copending application Serial No. 110,660, filed November 13, 1936, by Edwin L. Harder, William A. Lewis and myself.

The principal object of my invention is to provide an improved ground-preference system whereby preference may be given to the control of carrier-current, or, in general, current in a pilotchannel, in response to ground-faults (or phasefaults if desirable) without resort to a special ground-preference relay in addition to the usual ground and phase-fault-responsive relays which are otherwise required by the protective system.

A further object of my invention is to provide an intermittent-carrier relaying system having a normally non-tripping receiver-relay with means tending to move the receiver-relay to its tripping position in response to detector-super vised directional elements.

With the foregoing and other objects in view, my invention consists in the circuits, apparatus, systems, combinations and methods hereinafter described and claimed, and illustrated in the accompanying drawings wherein:

Figure 1 is a simplified diagrammatic view of circuits and apparatus embodying my invention in one preferred form of embodiment, features which are unnecessary to an understanding of my invention being omitted for the sake of clearness;

Fig. 2 is a so-called across the line diagram of the directcurrent connections of the same relaying system as that shown in Fig. 1, except that the CSP and CSG relay-coils are connected to the negative terminal through the auxiliary contact 9 of the circuit-breaker, which is a preferred connection; and

Fig. 3 is a fragmentary view similar to Fig. 2, illustrating a modification.

As shown in Fig. 1, my invention is illustrated as being applied to the protection of one end of a protected line-section 4 of a three-phase transmission line, only one end of the protected section being illustrated as the other end may be similar thereto, in its relaying equipment. The protected line-section 4 is energized from a power transformer bank 5, the secondary side of which is grounded as indicated at 6, and the primary side of which is energized by a synchronous dynamo-electric machine or generator G. It will be understood that other circuits or lines, similar to the line-section 4, and other loads or sources, will in general be connected to the illustrated end of the line-section, the simplest possible connections being illustrated for the sake of clearness.

Each end of the protected line-section 4 is provided with a line-sectionalizing circuit-interrupter I which may be an oil circuit-breaker provided with a trip-coil 8 and having auxiliary contacts 9 which are closed when the circuit-interrupter or breaker is closed.

My protective system, for controlling the tripping of the circuit breaker l, utilizes both linefrequency relays and a carrier-current system or other pilot-channel system for transmitting and responding to relaying signals to and from the other end of the protected line-section.

The line-frequency relays are illustrated as being energized from a group of line-current transformers H and potential transformers l2, and are arranged essentially in four panels I3, I 4, l5 and IS, the first three of which are phase-tophase relays and the last of which is composed of ground protective relays, and in addition, I utilize certain auxiliary relaying equipment which will be subsequently described.

The carrier-current equipment for the end of the line-section illustrated in Fig. 1 comprises a carrier-current transmitter l8 and a carriercurrent receiver-relay l9, both tuned to the same high or carrier-current frequency and both coupled to the protected line-section by means of a coupling transformer 2| and a coupling capacitor 22. In addition, it is necessary to provide a resonant carrier-frequency choke coil or wavetrap 23 in the line-wire to which the carrier is coupled, as indicated; and it is necessary to have a receiver-relay, marked RR, which responds to the receipt of suitable carrier-currents or signals.

The phase-fault line-frequency relaying equipments l3, I4 and I5 are all alike except that they are connected to be responsive to different phases of the transmission line, as indicated by the distinguishing subscripts A, B and C in the symbols designating the various relay elements, so that a description of the relay elements comprising the group I3 will suffice also for the groups [4 and IS.

The relay panel [3 utilizes three so-called instantaneous impedance relays which are set to respond to different distances or zones known as zones l, 2 and 3, as indicated by the symbols ZIA, ZZA and Z3A, the letter A indicating the phase in which the relay is connected. The balance-point of the first impedance element ZIA is necessarily within the length of the protected line-section, and is as close to the far end of the same as it is possible to make it without running the risk of a response to any fault-conditions which are further than the far end of the protected line-section. The second impedance element Z2A has its balance-point somewhere beyond the far end of the protected line-section and'usually, but not necessarily, in the next section beyond. The third impedance element 23A is still more sensitive, being set to respond to faults which are still more remote. Each of these impedance elements is provided with a current-.

responsive actuating coil 24 tendingto actuate the relay, and a voltageeresponsive restraining coil 25 tending to restrain the operation of the relay. The impedance relays ZIA and Z2A are shown as having their current coils 24 energized by the delta current, for the accurate measurement of impedance, as set forth in Goldsborough Patent No. 1,877,454, granted September 13, 1932, and in Lewis and Evans Patent No. 2,044,174, granted June 16, 1936. This delta current is in reality the difference between the line-currents in two of the phases of the protected section 4, said diiference being obtained by means of auxiliary current-transformers 28.

In the illustrated embodiment of my invention, the impedance relay Z3A has its current. coil 24 energized in response to the line-current in phase A, as distinguished from being responsive to a delta current. This is advantageous when certain kinds of out-of-step protection are added to the protective circuits, and it has the added advantage of relieving the burden on the auxiliary current-transformers 28.. I The voltage coils 25 of all three of the im pedance relays ZIA, 22A and 23A areenergized by the phase-tc-phase line-voltages, in the same phases to which the current coils of relays ZIA and ZZA respond, the voltage-coil potential being supplied by the potential transformer I2.

The relay panel l3 also comprises a so-called instantaneo directional element DA which is designated schematically as a wattmeter indicated by the letter W; a timing element which is designated schematically as a motor M, a mov-,

able arm 32 of which makes the successive contacts TZA and T3A for cooperating with the second and third-zone impedance elements Z2A and 23A respectively; an auxiliary relay or contactor-switch CSA; and also the previously mentioned auxiliary relay A for use in out-of-synchronism control. 7

The current-coil of the directional element DA is necessarily energized in response to the same current which'actuates the first and second-zone impedance elements ZIA and ZZA, this being necessary in order to prevent faulty operation of my relaying equipment.

The timer motor M is energized by any suitable means such as an auxiliary current-transformer 33 which is connected in series with any of the current coils 24 of this panel I3. In the illustrated form of embodiment, the current-transformer 33 is normally short-circuited by means of back-contacts 35 on the directional element DA, although this feature is usually not needed.

The timer motor M is connected to the currenta line-frequency current-flow in an internal direction, that is, from the transformer 5 into the protected line-section 4.

The ground-relay panel l6 comprises two socalled instantaneous ground-overcurrent relays IOH and IOL which are energized from the neutral of the line-current transformers These relays are of diiferent sensitivities, the first one being a high-current relay, as indicated by the letter H, and the second one being a more sensitive, low-current relay, as indicated by the nections for the directional element D0 are such that this relay element responds only for an finternal direction, that is, when the direction of the ground current issuch as to indicate that the; ground fault is on the same side of the power transformer 5 as the protected line-section '4.

The carrier-current transmitter I8 is illustrated. as being of a type having a master-oscillator tube 39. which is shown as being a triode comprising a cathode 45, a grid 4|, and a plate or anode 42. The oscillator-tube 39 is of such a type that the oscillations are blocked when a predetermined negative bias is applied to the grid 4| through the grid-control circuit 43, the cathode 40 being permanently connected to the positive stationbattery terminal I My receiver I9 is illustrated as comprising, inter alia, a receiver tube 44, having a cathode which is connected to the. negative terminal B ofthe B battery, and having a plate 46 which is connected to the plate-circuit or output-circuit 48 of the receiver. i My receiver-relay R is of special construction, an improved 'form of which is described and claimed in an application of B. E. Lenehan and A. W. Rogers, Serial No.'1l4,964, filed December 9, 1936. Some of the most essential features or" the receiver-relay are'indicated in Fig. 1 of my drawings, from which'it will be seen that the relay is of the polarized type, having a permanent magnet 5|l-at its base. The relay has a movable armature 5| of soft iron, which is pivoted by means of a spring-portion 52 which is connected to a central core 53 extending from the mid-point of the permanent magnet 50. Two special polepieces 54 and55 are provided for carrying the magnetic flux from the terminals of the permanent magnet to the front and back sides, respectively, of the armature 5|, the pole-pieces 54 and being preferably slightly separated, magnetically, from the ends of the permanent magnet 50, by means of shims or spacers 56 of brass or other non-magnetic material.

The central core 53 of the receiver-relay RR is provided with two coils, namely a trip coil marked RRT and a blocking or holding coil marked HRH. The trip coil RRT is adapted to be energized in such direction as to produce an operating force tending to move the armature 5| away from a back-stop 58, so as to make two sets of front-contacts 59 and B0. The blocking coil RRH "is more powerful than the tripping coil RRT and is designed to beenergized in such direction that it will tend tohold the armature back against its back-stop 58. In addition to these two forces, the receiver relay also has a continuously operative biasing torque which is provided, partly by the spring pivotal connection 52, and partly by an off-center mounting of the movable armature 5| between the faces of the two polepieces 54 and 55, so that the armature is normally a little bitv nearer to the back pole-piece 55, thereby developing a magnetic force tending to hold the armature 5i against its back-stop 58 as aresult of the magnetism of the permanent magnet 50.

The operating connections of the various parts of my system are shown in both Figs. 1 and 2, and may perhaps best be followed with reference to Fig. 2, although the connections may be traced in either figure. The station battery is indicated only in Fig. 1, near the circuit-breaker I, where it is designated by the numeral 6|. It is provided with a positive terminal and a negative terminal and it is indicated in Fig. 2 only by means of its two terminals and respectively.

Starting at the top of Fig. 2, it will be noted that the directional element DA is provided with a make-contact which establishes a partial circuit from the positive terminal to a phasedirectional bus 62A. Connected to the phasedirectional bus 62A is one terminal of a makecontact carried by the first impedance element ZIA, the other terminal of which is connected to a tripping bus 63T, which is connected to the trip-coil 8 ofthe circuit breaker, and thence,

through the auxiliary circuit-breaker contact 9 to the negative bus Beforev proceeding further with the next contacts shown at the top of Fig. 2, it is necessary to refer further down in the figure, where it is seen thatthe operating coil of the auxiliary relay CSA is connected between a so-called phase-fault carrier-starting bus 64 and the negative terminal through a resistor 65, also designated RA in Fig. 2 in order to distinguish this resistor from the corresponding resistors RB and RC in the other phases.

The phase-fault carrier-starting bus 64 is energized from the. positive terminal (-1-) by means of the closure of normally open or make contacts of any one of the three third-zone phasefault impedance-elements Z3A, Z3B or 23C. The operating coil of the relay-GSA is normally shortcircuited by a back-contact of the third-zone impedance element Z3A. .Said operating coil of the relay CSA is connected, on one side, through the resistor EA, to the negative bus and is connected, on the other side, to the phase-fault carrier-control bus 64. The phase-fault carrierstarting bus 64 is energized by the response of any one of the three third-zone impedance-elements Z3A, 233 or Z3C, this energization of the bus being promptly and directly effected by the closure of the front contact of the actuated element Z3A, Z313 or Z30, and this front contact, which initially energizes said bus 64, will be immediately bypassed by amake-contact of the corresponding auxiliary contactor-switch or relay CSA, CSB or CSC as the case may be. The operating coil of the CSA relay (for example) is normally shunted by a closed back-contact of the Z3A relay, so that this CSA relay. cannot operate unless its particular associated Z3A relay responds to faults on the transmission system.

Referring, now, to Fig. 1 it will be seen that the CSA relay, through its make-contacts 36, controls the energization of the timer motor M which is associated with the timer contacts HA and T3A. The starting of the timer motor M is dependent, also, upon a response of the internal directional element DA, which response is necessary in order to remove the short-circuit at the back contacts 35 of the directional element. It will be seen, therefore, that as soon as the third impedance element 23A and the directional element DA respond, the auxiliary relay CSA is energized, starting the timer motor M which in predetermined times first closes its timer contact T2A, and later on, its timer contact T3A.

Referring again to the top portion of the acrossthe-line diagram in Fig. 2, it will be seen that there is a second energizing circuit for the tripping bus 6ST from the phase-directional bus 62A through the front contact of the second impedance element ZZA and thence through the timer contact HA. The purpose of this energizing circuit is to provide for what is known as sequential tripping in the event that the carrier-current system is not utilized or is out of operation; that is, if there is a fault on the protected line-section very close to the far end of the line-section, so that the first impedance element ZIA will not respond, the fault will not be cleared at the relaying station under consideration until the elapse of a certain time determined by the TZA contact, which will provide ample time for the fault to be cleared by the instantaneous tripping element ZiA at the beginning of the next adjacent linesection (not shown) if it should be that the fault were just beyond the end of the line-section 4 rather than just before the end of the linesection 4. Meanwhile the fault is instantaneously cleared at the far end of the protected line-section by the ZIA tripping contact at that end, thereby resulting in the sequential tripping of the fault, first at the .end which is closest to the fault, and second at the end where the fault is so far away that the first-zone impedance relay element cannot discriminate between faults lying in the very extreme end of the line-section and faults occurring in the beginning of the next adjacent line-section beyond the section which is being protected. 1

The partial tripping circuits which may be traced through the directional and impedance contacts DA and Z2A in each of the three single-phase, phase-fault-responsive relaying elements, that is, including the partial tripping circuits provided by the make contacts of DB-Z2B and DC-Z2C, are bussed together by means of a phase-fault bus 69 which is thus energized whenever there is a phase-to-phase fault across any two of the line conductors of the line-section 4, close enough to energize the second impedance element of the corresponding line-frequency phase-relays, if, at the same time, the fault-current is in the internal direction, so as to pick up the corresponding directional element DA, DB or DC in that particular phase.

Asis previously known in carrier-current protectivesystems, and as shown in Figs. 1 and 2, I utilize a make-contact 59 of my receiver-relay HR to directly connect the phase-fault bus 69 with the tripping bus 853T under the control of carrier, so that the carrier-current protection may be utilized to discriminate between the faults which are just beyond the end of the protected line-section and faults which are just within the end of the protected line-section, so as to eliminate the timing element provided by the T2 end of the line-section. measure must be provided for ground faults as tacts of the third-zone impedance element 23A and the longtime contacts TBA which eventually complete a circuit directly from the p-hase-directional bus 62A to the tripping bus 63T, thus providing backup protection in the event that the fault is not properly cleared by relays at other stations which are closer to the fault, before the elapse of the time-setting of the T3A contacts.

"It will be understood that the foregoing description, which is mainly directed to the linefrequency phase-fault relay-panel i3, is equally applicable to the other two phase-panels I4 and IS, with a change of subscript to designate the B or C phases rather than the A phase. The particular system shown in the drawings includes a novel form of ground-fault protection which is the subject-matter of an application of Edwin L. Harder, Serial No. 177,560, filed concurrently herewith. This ground-protection system comprises separate ground-fault tripping and carrier-starting relays IOH and IOL, respectively, the latter being the more sensitive, that is, picking up at a lower value of the neutral or residual current. For simplicity of illustration; I have shown only the pilot-supervised ground-fault tripping-circuit including the make contacts of the ground directional relay DO and the high-current ground relay IOH, which together energize an intermediate bus 12, whichis'in turn connected, by the make contacts 60 of the receiver-relay RR, directly to the tripping bus 63T which is connected to the trip coil 8.

The particular system which I have illustrated also utilizes a novel form of grid-bias control which is more specifically claimed in the companion Harder application for starting the carrier-current transmitter i8 in such a manner thatthe fault-detectors for starting the carriercurrent transmission .are separate from the faultdetectors which cause tripping under carrier current control, that is, separate from the faultdetectors which have tripping contacts in series with the receiver-relay contacts 59 and B0; and these carrier-starting fault-detectors are set for a lower operating value than the aforesaid carrier-supervised tripping-circuit fault-detectors, for both phase and ground faults. Thus, the phase-fault carrier-starting bus 64 is energized by a response of any one of the third-zone impedance relays Z3A, 23B or ZSC, which are more sensitive than the corresponding carrier-supervised trip-circuit second-zone impedance relays ZZA, ZZB and Z20 which energize the phase-fault bus 69 in the tripping circuit. In like manner, the carrier-starting low-current ground-fault relay IOL is more sensitive than the carrier-supervised trip-circuit high-current ground-fault relay IOH which energizes the intermediate bus 12 in the tripping circuit. This precaution is for the purpose of insuring that the carrierstarting element or relay at one end of the protected line-section always functions at the saine time as, or prior to, the operation of the tripcircuit fault-responding element at the other This precautionary well as for phase faults.

It is frequently necessary to provide preferential control, which is vested in either the ground-fault relays or the phase-fault relays dications of the phase-current directional elements as a result of load-currents flowing in a direction opposite to the ground-fault currents on certain types of transmission systems. On the other hand, in some cases it may be desirable, to give the phase-relays preference over the ground-relays, or to have no preference at" all. Usually, however, ground-preference is desired, in order to properly relay in response to singlephase ground-faults, notwithstanding the fact that this ground preference would block the carrier-controlling function of the phase-relays in case of a double line-to-ground fault, or simultaneous ground-faults at two different locations in a protected line section.

According to my invention, I provide this preferential action, of whichever kind is desired, usually ground-preference, in an improved manner which does not necessitatethe utilization of a separateground-preference relay for this purpose. Thus, referring to the lower portion of Fig. 2, it will be noted that the transmitter-grid M is controlled by means of three serially connected resistors RI', R2 and R3, the resistor RI being closest to the grid. The third resistor R3 is normally connected to the negative bus (1) through the phase-fault carrier-control bus Gland the three parallels-connected resistors RA, RB and RC, thus making the grid negative;

The transmitter grid 41 is thus negatively biased, so as to block transmission, in the normal state of affairs, that is, when there is no fault on the transmission line.

In the event of a phase-fault on the trans-' elements Z2A, ZZB or also the corresponding phase-directional element or elements DA, DB or DC, thus energizing the, phase-fault bus 69, which in turn energizes the operating coil of an auxiliary phase-fault con- .tactor-switch or relay CSP, theother terminal of which is connected to the negative bus through the auxiliary contact 9 of the circuit,

breaker. This CSP relay picks up quickly and closes its make contacts, one of which is connected between the negative bus and. the

junction 18 between the resistors R2 and R3."

This causes the resistor R2 to become negative again, thereby applying a negative 'bias to the transmitter grid 4| and stopping the transmission of carrier-current. 7

If aground-fault occurs on the transmission system, the sensitive carrier-starting groundfault relay IOL will make a connection between negative, initiating the positive bus and the junction between the resistors'Rl and R2 thus making the resistor Rl positive, regardless of the condition of the phase-fault control-points G4 and 18, thus providing ground-fault preference. When the point 80 is made positive, the transmitter grid 41 is positive and carrier-current is transmitted. If the ground-fault is of sufficient intensity to pick up the less sensitive ground-fault relay IOH, which may be regarded as corresponding" in scope to the second-zone phase-fault impedance elements ZZA, ZZB and Z20, and if, at the same time, the direction of the ground-current is such as to indicate that the ground-current is flowing away from the relaying terminal under consideration and into the protected line-section, the ground directional element D will also pick up, thereby energizing the intermediate bus [2, connecting said bus to the positive terminal I have provided a ground-fault contactor-switch or relay CSG, the operating coil of which is connected between this intermediate bus 12 and the auxiliary breaker-switch or contact 9|, which is connected to the negative bus This CSG relay immediately picks up and closes its make contacts, one of which is connected between the grid-terminal 43 of the transmitter 18 and the negative bus thus making the grid 4| negative again, and blocking the transmission of carrier, regardless of all other controls on the carrier-current transmitter l8, thus providing again for groundpreference.

As shown at the bottom of Fig. 2, the two coils RRH and RRT of the receiver-relay RR are controlled as follows. The holding or blocking coil RRH is connected between the positive B-battery terminal B+ and the plate circuit 48 of the receiver IS, SO that this coil RRI-I is energized whenever the receiver I9 receives a suflicient amount of carrier-current energy from the transmitter H3 at either end of the protected line-section. The tripping coil RRT of the receiver-relay RR is con-- nected, on one side, to the positive bus and on the other side it may be connected to the negative bus by one of the make-contacts of either of the CSP or CSG relays, which respond to internal phase-faults and internal groundfaults, respectively. In this way, the tripping coil RRT of the receiver-relay is not energized until both an insensitive fault-detector response Z2A, ZZB, Z20 or IOH, and a directional response DA, DB, DC or D0, are obtained, which takes longer than a sensitive non-directional fault response Z3 or IOL. The sensitive fault-detectors Z2 and IOI-I require more current, to operate them, and thus are not only slower than Z3 and IOL, for any given fault-current, but also sometimes may not operate at all for fault-currents which are just barely suflicient to operate Z3 or IOL. The energization of the tripping coil RRT is still further delayed by the slight operatingtime required by the auxiliary relay CSP or CSG, as the case may be. Thus an ample factor of safety is provided, to make sure that the holding coils RRH shall be energized, at both ends of the protected line-section, before either tripping coil RRT can possibly be energized.

It is believed that the operation of my carriercurrent or pilot-channel relaying equipment will be obvious from the drawing and from the foregoing description. The receiver relay RR is normally biased to its illustrated position, with its movable element against the back-stop 5B, and with its front-contacts 59 and 60 open. If a 75" the sensitive fault-detector Z3 or IOL, as the case may be, to operate, changing the transmitter grid 4| from a negative 'bias to a positive potential, and starting the transmission of carrier. This immediately puts carrier on the protected line-section and operates the receiver-relay holding coils RRH at both ends of the line-section, thus insuring that the receiver-relays RR shall remain in their normal non-tripping positions, regardless of whether their operating or tripping coils RRT are energized or not.

' If there is a fault .within the reach of the second-zone impedance element Z2 or the insensitive ground element IOH, accompanied, in either case, by-an internal direction, or direction into the protected line-section, the auxiliary relay CSP or CSG at the terminal where this internal direction occurs will be operated, closing its make contacts CSP or CSG and energizing the operating or tripping coil RRT of the receiver relay RR at that station. At the same time, the same relay CSP or CSG, as the day may be, will change the transmitter grid-bias so as to block transmission of carrier-current at that station. Unless, however, there is a similar internal direction registered at the other end or ends of the protected line-section, carrier-current will not be removed from the line-section at said end or ends, so that the receiver-relay holding-coils RRH will remain energized at both or all ends of the line-section, thus preventing the closure of either one of the receiver-relay tripping-contacts59 or 60. If the direction is internal at both or all ends, carrier will be altogether removed from the line-section, the receiver-relay holding-coils RRI-Iwill be deenergized, and the receiver-relay tripping-coils RRT will actuate the respective receiver-relays RR to their tripping positions, closing their contacts 59 and 6D in the trip-circuits.

A modified form of the carrier-transmitter control is illustrated in Fig. 3, which is intended to replace the bottom portion of the Fig. 2 diagram, below the make-contact of the CSG relay. In this modification, which, in some respects may be preferred to the one which is shown in Figs. 1 and 2, I utilize back-contacts on the sensitive fault-detectors for initiating the carriercurrent transmission by changing the grid-bias from. negative to positive, thereby starting the carrier a little more quickly than in the Fig. 2 modification in which frontor make-contacts were utilized for this purpose. This quick starting of the carrier is, or may be, frequently desirable in some systems in which there are conditions in which it is difficult to coordinate the speeds of operation or the pick-up points of the relays at the two ends of the protected line-section, to make certain that carrier shall be transmitted, from one end, thus blocking tripping, before the tripping-circuit can be set up through the receiver-relay tripping contacts 59 or 60 at the other end.

In the relaying system shown. in Fig. 3, the sensitive ground-fault detector IOL is provided with a back-contact 9| instead of having a frontcontact as in Fig. 2; and the sensitive phasefault detectors Z3A, Z3B and Z30 have additional back-contacts 92, in addition to the contacts which are required in the embodiment of my invention which is shown in Figs. 1 and 2. In Fig. 3, the phase-fault bus 64 is not utilized in the control of the transmitter, and the resistors RI, R2 and R3 are replaced by a single resistor R.

The grid-circuit of the transmitter-tube 39 starts, as before, with the grid lead 43; and, as

before, the first contact-which is made to this grid-circuit, at a point close to the grid 4|, that is, in a connection to the grid-lead 43, is a connection through the make-contact of the CSG relay, which makes certain, regardless of any other controls, that the grid shall be connected to the negative bus whenever the CSG relay picks up in response to ground-faults with an internal direction.

From this point on, however, the connections are different fromthose in Fig. 2. The resistor R, in Fig. 3, is connected between the grid-lead 43 and the positive bus but the grid-lead is normally held to a negative potential by being connected. through the four fault-detector back-contacts 9| and 92, all connected in series between the grid-lead 43 and the negative bus The three phase-fault-detector back-contacts 92 of the impedance elements Z3A, 23B and 230 are shunted by'the CSP make-contact which responds to a phase-fault condition accompanied by an internal direction of currentflow. This CSP make-contact is thus in series with the ground-detector contact 9|, so that when theground-detector contact 9| is open, in response to a ground-fault, a subsequent closure of the CSP make-contact will not have any effect at all upon the potential of the transmittergrid 4|. I

The Fig. 3 control operates as follows. Normally, the grid 4| is connected to the negative bus through the back-contacts SI and 92 of the four sensitive fault detectors IOL, Z3A, 23B and Z30. If any one of these fault-detectors responds, the negative connection is broken,

and the resistor R'immediately brings the grid to the potential of the positive bus If the ground-fault detector IOL responds, not only is the grid made positive, starting. carrier-current transmission, but the phase-fault directionally responsive relay CSP is also rendered. powerless thereafter to make the grid negative and stop the carrier-current transmission. If the groundfault directionally responsive relay CSG responds, the grid is made negative, stopping the my invention. I desire, therefore, that the ap pended claims shall be accorded the broadest construction consistent with their language and the prior art.

I claim as my invention 1. Preferential relaying equipment for an alternating-current transmission-line, .including a signal-current pilot-channel between the ends ofa line-section .to be protected, and further including, at each of said ends, a circuit-interrupter means and trip-circuit means for actuating said circuit-interrupter means, including two dif- V ferent kinds of fault-responsive relaying means, one of said responses being a preferential-fault response, and the other being an other-faultresponse, each of said fault-responsive relaying means including both a fault-detector relaying means and a directional relaying means operative less rapidly than its corresponding fault-detector relaying means, a signal-current receiver, and a fourth impedance-portions.-

signal-current transmitter, characterized by said transmitter having a grid-controlled tube, and

controlling means for normally supplying a blocking potential to said grid-circuit during normal. operating conditions of said transmission line, said controlling means including, in combination,

a source of biasing potentials, an impedance;

device, and four circuit-make-and-break means controlled by different ones of said four relaying means, including the following arrangement, in

combination; a first means, connected in said,

on whenever, and only whenever, said preferential-fault detector means responds, andwhen, and

only when, said first means is non-responsivaregardless of any other-fault responses; a third means, connected in said grid-circuit in a manner different from said first means, and in such man ner as to make sure that said grid hasa blocking potential thereon when, and only when, said first and second means are non-responsive and when,

and only when, said other-fault directional means responds; and a fourth means, connected in said I grid-circuit in a manner different from either said first or second means, for makingsurethat" said grid has a non-blockingpotential thereon in response to a response of said other-fault detector means when; and only when, neither said first nor third means is operative toapply a block ing potential to the grid. V v 2. The invention as defined in claim 1, characterized by a grid-circuit comprising four 'im pedance-portions serially connected between'the grid and the source ,of blocking potential, the

first impedance-portion being closest to the grid, said second means being operative to complete a circuit between the source of non-blocking;po-

tential and the junction between the" first and second impedance-portions, said third means being operative to complete a circuit between the source of blocking potential and the junction between the second and third impedance portions, and said fourth means being operative to complete a circuit between the source of non-blocking potential and the junction between the third an 3. The invention as defined in claim 1, characterized by said impedance-device being connected between the grid and the source of nonblocking potential, and said second and fourth means being serially connected normally closed relay-contacts.

4. The invention as defined in claim 1, characterized by said impedance-device being con- 'nected between the grid and the source of nonblocking potential, said second and fourth means being serially connected normally closed relaycontacts, and said third means being a normally open relay-contact connected said fourth means.

5. The invention as defined in claim '1, characterized by each of said directional relaying means comprising a sensitive directional element and a fault-detector element, both responsive to the same kind of currents, and con nections whereby both of said elements must respond before said directional relaying means will indicate a response, said fault-detector element being less sensitive than its associated fault-dein shunt around} tector relaying means which controls the transmitter grid-potential.

6. The invention as defined in claim 1, characterized by said transmission line being polyphase, one kind of fault-responsive means being phase-fault responsive, the other kind being ground-fault responsive, the phase-fault directional relaying means comprising a plurality of pairs of single-phase elements connected in different phases, one of said elements of each pair being a sensitive directional element and the other being a fault-detector element, both responsive to phase-to-phase currents in the same delta phase, the ground-fault directional relaying means comprising a pair of elements, one being a sensitive ground-fault directional element and the other being a ground-fault detector element, and connections whereby both of the elements of some pair must respond before the corresponding directional relaying means will indicate a response, each fault-detector element being less sensitive than its associated fault-detector relaying means which controls the transmitter gridpotential.

7. Preferential relaying equipment for an alternating-current transmission-line, including a signal-current pilot-channel between'the ends of a line-section to be protected, and further in cluding, at each of said ends, a circuit-interrupter means and trip-circuit means for actuating said circuit-interrupter means, including two different kinds of fault-responsive relaying means, one of said responses being a preferential-fault response, and the other being an other-fault response, each of said fault-responsive relaying means including both a fault-detector relaying means and a directional relaying means operative less rapidly than its corresponding fault-detector relaying means, a signal-current receiver, and a signal-current transmitter, characterized by said transmitter having a grid-controlled tube, and controlling means for normally supplying a blocking potential to said grid-circuit during normal operating conditions of said transmission line, said controlling means including, in combination, a source of biasing potentials, an impedance-device, and a plurality of contact-means controlled by different ones of said four relaying means, including the following arrangement, in combination; first contact-means, connected in said grid-circuit at a point close to the grid, for making sure that the grid has a blocking potential thereon Whenever, and only whenever, said preferential-fault directional means responds, regardless of any other responses; second contact-means so connected in said grid-circuit as to make sure that the grid has a non-blocking potential thereon whenever, and only whenever, either one of said detector-means responds, and

when, and only when, said first contact-means is non-responsive; and third contact-means, connected in said grid-circuit in a manner different from said first contact-means, and in such manner as to make sure that said grid has a blocking potential thereon when, and only when, said terized by each of said directional relaying means comprising a sensitive directional element and a fault-detector element, both responsive to the same kind of currents, and connections whereby both of said elements must respond before said directional relaying means will indicate a response, said fault-detector element being less sensitive than its associated fault-detector relaying means which controls the polarity of said signal-current control-means. I

lOrThe invention as defined in claim 7, characterized by said transmission line being polyphase, one kind of fault-responsive means being phase-fault responsive, the other kind being ground-fault responsive, the phase-fault directional relaying means comprising a plurality of pairs of single-phase elements connected in different phases, one of said elements of each pair being a sensitive directional element and the other being a fault-detector element, both responsive to phase-to-phase currents in the same delta phase, the ground-fault directional relaying means comprising a pair of elements, one being a sensitive ground-fault directional element and the other being a ground-fault detector element, and connections whereby both of the elements of some pair must respond before the corresponding directional relaying means will indicate a response, each fault-detector element being less sensitive than its associated fault-detector relaying means which controls the polarity of said signal-current controlmeans.

11. Preferential relaying equipment for an alternating-current transmission-line, including a signal-current pilot-channel between the ends of a line-section to be protected, and further including, at each of said ends, a circuit-interrupter means and trip-circuit means for actuating said circuit-interrupter means, including two different kinds of fault-responsive relaying means, one of said responses being a preferential-fault response, and the other being an other-fault response, each of said fault-responsive relaying means including both a fault-detector relaying means and a directional relaying means operative less rapidly than its corresponding fault-detector relaying means, a signal current receiver, and signal-current control means comprising an impedance device, a source of potentials of a first polarity and a different second polarity, means for normally connecting said signal-current control-means to said first polarity during normal fault-free operating-conditions of the transmission line, first circuit-controlling means associated with said impedance device and source in a manner such as to assure that said signal-current control-means has said first polarity whenever, and only Whenever, said preferential-fault directional means responds, regardless of any other responses; second circuit-controlling means associated with said impedance device and source in a manner such as to assure that said signal-current control-means has said second polarity whenever, and only whenever, said preferential-fault detector-means responds, and when, and only when, said first circuit-controlling means is non-responsive, regardless of any other fault responses; third circuit-controlling means associated with said impedance device and source in a manner such as to assure that said signal-current control-means has said first polarity when, and only when, said first and second circuit-controlling means are non-responsive and when, and only when,said other-fault directional means responds; and fourth circuit-controlling means associated with said impedance device and source in a manner such as to assure that said signal-current control-means has said second polarity in response to a response of said other-fault detector-means when, and only when,

circuit between the first-polarity source and the junction between the second and third impedance-portions, and said fourth circuit-controlling means being operative to complete a circuit between the second-polarity source and the junction between the third and fourth impedance-portions.

- 13. The invention as defined in claim 11, characterized by said impedance-device being connected between said signal-current control-means and the second-polarity source, and said second and fourth circuit-controlling means being normally closed relay-contacts.

l4. Theinvention as defined in claim 11, characterized by said impedance-device being con nected between said signal-current control-means and the second-polarity source, said second and fourth circuit-controlling means being normally closed relay-contacts, and said third circuit-controlling means being a normally open relay-con- "tact connected in shunt around said fourth circult-controlling means.

15. The invention as defined in claim 11, characterized by each of said directional relaying vmeans comprising a sensitive directional element "and a fault-detector element, both responsive to the same kind of currents, and connections whereby both of said elements must respond before said directional relaying means will indi- I cate a response, said fault-detector element being "less sensitive than its associated fault-detector relaying means which controls the polarity of said signal-current control-means.

16. The invention as defined in claim 11, characterized by said transmission line being poly- "phase, one kind of fault-responsive means being phase-fault responsive, the other kind being ground-fault responsive, the phase-fault direction relaying means comprising a plurality of pairs of single-phase elements connected in different phases, one of said elements of each pair being a sensitive directional element and the other being a fault-detector element, both responsive to phase-to-phase currents in the same delta phase, the ground-fault directional relaying means comprising a pair of elements, one being a sensitive ground-fault directional element and the other being a ground-fault detector element, and connections whereby both of the elements of some pair'must respond before the corresponding directional relaying means will indicate a response, each fault-detector element being less sensitive than its associated fault-detector relay ing means which controls the polarity of said signal-current control means.

17. Preferential relaying equipment for anal ternating-current transmission-line, including a' signal-current pilot-channel between the ends of a line-section to be protected, and further including, at each of said ends, a circuit-interrupter means and trip-circuit means for actuating said circuit-interrupter means, including two different kinds of fault-responsive relaying means, one of said responses being a preferential-fault response,

and the other being an other-fault response, each of said fault-responsive relaying means including both a fault-detector relaying means and a directional relaying means operative less'rapidly than its corresponding fault-detector relaying means, a signal-current receiver, and signal-current control-means comprising an impedance device, a source of potentials of a first polarity and a different second polarity, means for normally connecting said signal-current control-means to said first polarity during normal fault-free operating conditions of the transmission line, first circuitcontrolling means, associated with said imped ance device and source in a manner such as to, assure that said signal-current control-meanshassaid first polarity whenever, and only whenever,

said I preferential-fault directional means re-' sponds, regardless of any other responses; second circuit-controlling means associated with said impedance device and source in a manner. such as to assure that said signal-current control-means has said second polarity whenever and only whenever either one of said detectormeans responds, and when, and only whensaid first circuit-controlling means is non-responsive;- and third circuit-controlling means'associated with said impedance device and source in a manner such as to assure that said signal-current control-means has said first polarity when, and only when, said first circuit-controlling means and said preferential-fault detector-means are both non-responsive and when, and only when,-said other-fault directional means responds.

18. The invention as defined inclaim 17, char-' acterized' by said impedance device being connected between said signal-current control-means and thesecond-polarity source, and-said second circuit-controlling means being normally closed contact-means.

19. The invention as defined in claim 17, characterized by each of said directional relay means comprising a. sensitive directional element and a fault-detector element, both responsive to the same kind of currents, and connections whereby both of said elements must respond before said directional relaying means will indicate a response, said fault-detector element being less sensitive than its associated fault-detector relaying means which controls the polarity ofsaid signal-current control-means.

20. The invention as defined in claim 17, char- 7 and connections whereby both of the elements of some pair must respond before the corresponding directional relaying means will indicate a response, each fault-detector element being less sensitive than its associated fault-detector relaying means which controls the polarity of said signal-current control-means.

21. Relaying equipment for an alternatingcurrent transmission-line, including a signalcurrent pilot-channel between the ends of a linesection to be protected, and further including,

at each of said ends, a circuit-interrupter means and trip-circuit means for actuating said circuitinterrupter means, including a fault-detector relaying means and a directional relaying means both responsive to the same kinds of faults on the transmission-line, a normally non-transmitting signal-current transmitter, means responsive to a response of said fault-detector relaying means for initiating the operation of said signalcurrent transmitter, a signal-current receiver, and a receiver-relay having a trip-circuit contact, means for holding said receiver-relay in a non-tripping position during normal fault-free operating conditions of the transmission line, means responsive to a receipt of sufficient signalcurrent by said receiver for blocking movement of said receiver-relay to its tripping position, and means responsive to a response of said directional relaying means for nullifying the transmitter-controlling action of said fault-detector relaying means and for causing said receiverrelay to move to its tripping position in the absence of said blocking action, characterized. by said directional relaying means comprising a sensitive directional element and a fault-detector element, and connections whereby both of said elements must respond before said directional relaying means will indicate a response, said fault-detector element being less sensitive than said fault-detector relaying means.

22. The invention as defined in claim 21, characterized by said transmission-line being polyphase, and said trip-circuit means comprising a plurality of pairs of phase-fault single-phase fault-detector relaying means and phase-fault single-phase directional relaying means, as defined, for the respective phases.

23. The invention as defined in claim 21, characterized by said transmission-line being polyphase, and said trip-circuit means comprising a plurality of pairs of phase-fault single-phase fault-detector relaying means andv phase-fault single-phase directional relaying means, as defined, for the respective phases, the two elements of each phase-fault directional relaying means being both responsive to the same kind of currents.

24. The invention as defined in claim 21, characterized by said transmission-line being polyphase, and said trip-circuit means comprising a plurality of pairs of phase-fault single-phase faultdetector relaying means and phase-fault single-phase directional relaying means, as defined, for the respective phases, and another set of ground-fault-detector relaying means and ground-fault directional relaying means, as defined, for ground-fault protection, said phasefault and ground-fault relaying means provid ing, one a preferential-fault response, and the other an other-fault response, and means whereby, when said preferential-faultdetector relaying means is operative to cause the operation of said signal-current transmitter, said other-fault directional relaying means shall be inoperative to block said operationv of said signal-current transmitter.

25. Relaying equipment for an alternatingcurrent transmission-line, including a signal-current pilot-channel between the ends of a linesection to be protected, and further including, at each of said ends, a circuit-interrupter means and trip-circuit means for actuating said cir- Gu lt-interrupter means, including a phase-faultdetector relaying means and a phase-fault directional relaying means responsive to line-to-line faults on the transmission-line, a normally nontransmitting signal-current transmitter, means responsive to a response of said fault-detector relaying means for initiating the operation of said signal-current transmitter, a signal-current receiver, and a receiver-relay having a trip-circuit contact, means for holding said receiverrelay in a non-tripping position during normal fault-free operating conditions of the transmis sion line, means responsive to a receipt of sufficient signal-current by said receiver for blocking movement of said receiver-relay to its tripping position, and means responsive to a response of said directional relaying means for nullifying the transmitter-controlling action of said fault-detector relaying means and for causing said receiver-relay to move to its tripping position in the absence of said blocking action, characterized by said directional relaying means comprising a sensitive directional element and a fau1tdetector element, and connections whereby both of said elements must respond before said directional relaying means will indicate a response.

BERNARD E. LENEHAN. 

